Underweight women were 1.2 times more likely to have significant complications, while overweight women showed a steady weight-related increase in risk up to 1.4 times that of their normal-weight counterparts.

Queensland obstetrician Gino Pecoraro told The Courier-Mail that the findings were relevant to Australian women.

Kate Wright wants to do everything she can to make her pregnancy go smoothly.

"What women eat in pregnancy has been known to be important for some time, perhaps it is now important for women to watch how much they eat," Dr Pecoraro said.

"While the study is not able to say that the increased weight caused the complications, it does suggest a statistically significant association, which makes trying to keep weight in check very worth while."

Kate Wright, of the Gold Coast, is 25 weeks pregnant with twins. Before her pregnancy she was a body builder.

"Because of my background I carry a lot of muscle mass, and that can really throw off the BMI reading so I don't live my life based on BMI, but I do believe in eating healthy and keeping healthy," she said.

"I went through IVF to have my babies and I want to do everything I can to try to make the pregnancy go smoothly."